Special Paper: What Determines the Probability of Discovering a Species?: A Study of South American Oscine Passerine Birds

Abstract

The spread of dates of description for species within taxa is normally broad, clearly indicating that there is considerable variation in the probability of species being discovered. The precise reason for this variation is unknown, although newly described species have been characterised as small, cryptic and locally distributed. Here, we explore the hypotheses that the range (both geographic and altitudinal), abundance and body size of species determine their probability of discovery, using South American oscine passerine birds. A species geographic range is the best predictor of its date of description: the two are strongly negatively correlated both across all species and within taxa, and when controlling for other variables. Altitudinal range and body mass are negatively correlated with date of description across species, and abundance and altitudinal range are negatively correlated with description date within taxa. However, the amounts of variation explained by these variables are low, and none of the variables remain significantly correlated with date of description if geographic range is controlled for using multiple regression. Of those variables tested, species body mass is the poorest predictor of species date of description, at least in South American oscine passerine birds. Whether the visual conspicuousness (e.g. plumage and behaviour) of a species affects its probability of description remains untested.